1. Field of Invention
The present invention relates generally to a device for diagnosing the body with ultrasonic waves and, more particularly, to an invasive ultrasound device.
2. Description of the Related Art
Non-invasive ultrasound techniques have been used for many years to produced detailed images of bodily structures. In a non-invasive procedure, a transducer is placed on the surface of the patient's body. An image is generated by producing an ultrasound signal with the transducer, receiving the reflected portion of the ultrasound signal with the transducer, and then transmitting a corresponding signal to a device which includes imaging circuitry and a display. In echocardiography, for example, a transducer is placed on the patient's chest and an image of the heart is produced.
In recent years, invasive ultrasound techniques have been developed. Here, a miniature ultrasound transducer is mounted on a catheter that is directed into the bodily structure of interest. The image shown on the display is a cross-section (or "slice") of that structure. One invasive ultrasound technique is intracardiac echocardiography. Here, a transducer is carried by a catheter into the patient's heart and the image shown on the display is a cross-section of the heart.
The inventor herein has determined that one disadvantage of conventional invasive ultrasound techniques is that the angular orientation of the displayed image is not fixed relative to an anatomical direction. Moreover, the image will often rotate as the transducer carrying catheter rotates relative to the patient. This rotation can be caused by operator handling of the catheter and the motion associated with cardiac and respiratory cycles. Despite the fact that physicians are familiar with the large scale anatomy of the heart and other organs, as well as the associated vascular structures, it is often difficult for them to place the displayed cross-sections within the context of the organ of interest. The physician must rely on his or her knowledge of bodily structures to first recognize the portion of the body being imaged. Once that task is completed, the physician must infer the rotational orientation of the image based on the typical orientation of that structure relative to the other portions of the patient's body.